Soil Aggregate Stability in Different Soil Orders Quantified by Low Dispersive Ultrasonic Energy Levels

Ultrasonic dispersion of soil aggregates in water-based solutions is commonly used in soil science, because it is possible to quantify the amount of energy applied to the solutions. However, currently available instrumentation does not provide precisely controlled low ultrasonic energy; thus, the study of weakly aggregated soils is still a challenge. The aim of this study was to apply amplitude controlled, low energy ultrasonic dispersion to study macroaggregate breakdown in soil orders with wide range of stabilities and formed on diverse parent materials: alluvial calcareous sediments (Entisol), volcanic ash and basalt (Andisol), serpentinite (Alfisol), schist (Ultisol), and granite (Inceptisol). Aggregates were exposed to increasing ultrasonic energy levels in six steps from 0 to 40 J mL(-1), and the resulting macro- and microaggregate masses were measured. Subsequently, the aggregate distribution was correlated with various physicochemical properties of the 250- to 1000-m macroaggregates. The study showed that aggregate breakdown at low energy levels was greatest in the Andisol and the Entisol, followed by the Alfisol, Ultisol, and Inceptisol. Stability of macroaggregates was influenced by particle-size distribution, the amounts of exchangeable Mn (influenced mean weight diameter [MWD] positively) and exchangeable Mg (influenced MWD negatively). In contrast, stable microaggregates in the range of 63- to 250-m were positively correlated with oxalate extractable Fe and Al as well as with soil organic matter (SOM) content. The results demonstrate that aggregate breakdown is strongly depending on the amount of energy applied, as well as of soil properties, which influence defined aggregate-size classes differently.